The present invention relates to a bearing device for supporting a wheel and equipped with braking means. The device includes a rotary shaft carrying a rotary plate suitable for supporting a wheel rim, a stationary hub disposed around the rotary shaft, a bearing unit comprising at least one rolling bearing supporting the shaft as it rotates relative to the hub, and braking means comprising a first series of at least one annular brake disk secured to the hub and a second series of at least one annular brake disk constrained to rotate with the shaft relative to the hub.
A device of this type is known from Document FR 2 606 092 which shows a motor having radial pistons and having a rotary shaft supported by bearings in a stationary casing. An end of the shaft that is situated outside the casing carries a rotary plate serving for fixing to the rim of a wheel. The motor includes a brake having xe2x80x9couterxe2x80x9d disks that are prevented from rotating relative to the casing by fluting provided in the inside periphery thereof, and xe2x80x9cinnerxe2x80x9d disks which are constrained to rotate with the shaft by fluting provided in an axial portion of said shaft. The brake is situated in a region of the motor that is of relatively small diameter so that, in order to obtain high braking torque, it is necessary to provide a large number of disks, which gives rise to a large overall axial size. In other words, for a limited axial size, enabling only a limited number of disks to be received, the braking torque is relatively low. In spite of that, the bearing portion of the motor and the plate for fixing to the wheel rim have a relatively large overall radial size, since the plate projects radially relative to that portion of the casing in which the brake is situated.
Document DE 32 22 261 shows a braked bearing that also has a rotary plate for fixing to the rim of a wheel. The rotary portion is also inside the casing, the plate lying outside said casing while lying within the overall axial size of the casing of the bearing unit. Once again, the xe2x80x9cinnerxe2x80x9d brake disks are secured to the rotary portion which is situated inside the casing, while the xe2x80x9couterxe2x80x9d disks are secured to the stationary portion that is prevented from rotating. The rotary portion which is secured to the inner disks is in the form of a sleeve secured to the plate. It is supported as it rotates relative to the stationary portion by a bearing unit which is situated between the inner periphery of the sleeve and the outer periphery of a second sleeve which is secured to the stationary portion.
The present invention proposes to improve the above-mentioned prior art by making it possible to obtain a braking torque that is higher within a limited axial size and by facilitating heat exchange between the brake and the outside.
This object is achieved by that facts that the device of the invention includes a first axial wall element forming a rotary brake ring constrained to rotate with the shaft relative to the hub and disposed around a portion of said hub that forms a second axial wall element, and that each disk of the second series is secured to the inner periphery of said rotary brake ring, while each disk of the first series is secured to the outer periphery of said second axial wall element surrounded by the rotary brake ring.
In the layout of the invention, the rotary portion of the brake formed by the ring secured to the shaft lies outside the bearing device. As a result, the brake can easily be disposed on a large diameter, so that its braking torque is significantly improved. In addition, the brake disk(s) that, via the ring, is/are constrained to rotate with the shaft lie on the outside. Thus, since the rotary portion of the brake lies on the outside, the exchange of heat between the brake and the surrounding environment is facilitated, thereby avoiding overheating of the brake disk(s) and of the fluid in contact therewith.
While providing braking on a large diameter, it is also possible to obtain a bearing device that is compact and whose flange supporting the rim of a wheel lies within the overall radial size of the device.
Advantageously, the disk(s) of the second series is/are of outside diameter greater than the outside diameter of the disk(s) of the first series, each disk of the second series co-operating via its outer periphery with the rotary brake ring, while each disk of the first series co-operates via its inner periphery with said second axial wall element surrounded by the rotary brake ring.
As a result the xe2x80x9couterxe2x80x9d disks, which are of larger diameter, are secured to the rotary portion of the brake.
In an advantageous layout, the device includes a stationary abutment member secured to the second axial wall element, the disks of the braking means being disposed between said abutment member and means forming a brake piston suitable for taking up a braking configuration in which an active piston portion is moved towards the abutment member to urge the brake disks into braking contact as well as a brake release configuration in which said active portion is moved away from the abutment member.
In the braking configuration, the active piston portion is pressed against the first brake disk, and the disks are clamped together (braking contact) between said active piston portion and the abutment member.
The brake piston is normally stationary, i.e. it is prevented from rotating. The fact that the abutment member is also chosen to be prevented from rotating makes it possible to ensure that, during braking, the disks of the two series are clamped between two elements that are prevented from rotating. Thus, the braking effect is obtained directly by the friction of the disks, and by the two stationary elements, without it being necessary for the thrust forces of the brake piston to be withstood by the rolling bearing(s) of the bearing unit, which rolling bearings take up the axial forces and the radial forces due to the rotation of the shaft relative to the hub. In other words, the stresses exerted on the bearing unit during braking are thus reduced.
Advantageously, the device includes a braking resilient return member suitable for co-operating with the brakepiston-forming means to urge said means continuously towards their braking configuration, a brake release hydraulic chamber suitable for being fed with fluid under pressure so as to urge the brakepiston-forming means towards their brake release configuration, and a braking hydraulic chamber suitable for being fed with pressurized fluid so as to urge the brakepiston-forming means towards their braking configuration.
The presence of the braking resilient return member makes it possible to provide a parking braking effect and an emergency braking effect, when, during abnormal operating, the fluid pressure that normally feeds the brake release hydraulic chamber decreases. The presence of the braking hydraulic chamber also makes it possible to perform in-service or dynamic braking, actuated positively by a pressurized fluid feeding the braking chamber. A multi-effect brake is thus obtained, in which the parking and emergency braking effect and the hydraulic brake release effect are combined with a dynamic braking effect.
In which case, it is advantageous for the brakepiston-forming means to comprise first and second pistons, the first piston having an active face suitable for co-operating directly with a first brake disk adjacent to said active face, the braking hydraulic chamber being defined between said first piston, a portion of the stationary hub referred to as the xe2x80x9cbrake supportxe2x80x9d, and the second piston, the second piston co-operating with the braking resilient return member, being mounted to slide relative to the first piston and relative to the brake support, and being suitable for coming into abutment against said first piston under the effect of the braking resilient return member so as to push the first piston against the first brake disk.
This layout makes it possible to make the above-mentioned multi-effect brake simply and compactly. In addition, dynamic hydraulic braking affects the first piston, while parking and emergency braking and brake release affect the second piston. As a result, the brake release hydraulic chamber and the braking hydraulic chamber are separate, so that the in-service braking forces are independent of the forces generated in the brake release chamber by the brake release fluid. Thus, during in-service braking, braking pressure does not have to displace all of the brakepiston-forming means and does not have to overcome the brake release force which is exerted on these means, but rather it acts on a portion only of the brakepiston-forming means (in this example, the first piston).
The first piston then advantageously has an annular extension extending on the side opposite from its active face, the extension being disposed between the brake support and a zone of the second piston that has an axial overlap relative to said brake support, and the braking chamber is defined between said annular extension, the brake support, and said zone of the second piston.
Thus, the separation and the sealing between the inservice braking chamber and the brake release chamber are provided by a simple layout.
The invention also provides an assembly constituted by a hydraulic motor including a rotary shaft disposed in a stationary casing, and by a bearing device of the invention for supporting a wheel, the casing of the motor constituting a portion of the stationary hub.
In the assembly of the invention, in addition to the fact that the bearing device has the above-mentioned characteristics, the motor is a hydraulic motor having radial pistons, and the fixed hub constitutes a casing portion of the motor.
The assembly is of small overall axial size. In addition, the rotary ring overlaps the second axial wall element formed by an axial portion of the stationary hub, which itself constitutes a casing portion of the motor.
In other words, a portion of the casing of the motor (the fixed hub) is surrounded by the rotary ring which is itself secured to the rotary plate. As a result, the plate may be of large diameter, which makes it possible to place the fixing of the wheel rim on a large diameter. The rim can be coupled directly to the fixing plate which is secured to the rotary ring. Regardless of whether or not the ring is made integrally with the plate, the connection between these elements is dimensioned to withstand both the braking torque and the drive torque on the wheel rim. In general, this assembly increases the rigidity of the fixing of the rim by direct coupling with the plate and with the rotary ring.